Prediction of Crosswind Separation Velocity for Fan and Nacelle Systems Using Body Force Models: Part 1: Fan Body Force Model Generation without Detailed Stage Geometry

Quentin J Minaker,Jeffrey J Defoe

doi:10.3390/ijtpp4040043

Abstract

Modern aircraft engines must accommodate inflow distortions entering the engines as a consequence of modifying the size, shape, and placement of the engines and/or nacelle to increase propulsive efficiency and reduce aircraft weight and drag. It is important to be able to predict the interactions between the external flow and the fan early in the design process. This is challenging due to computational cost and limited access to detailed fan/engine geometry. In this, the first part of a two part paper, we present a design process that produces a fan gas path and body force model with performance representative of modern high bypass ratio turbofan engines. The target users are those with limited experience in turbomachinery design or limited access to fan geometry. We employ quasi-1D analysis and a series of simplifying assumptions to produce a gas path and the body force model inputs. Using a body force model of the fan enables steady computational fluid dynamics simulations to capture fan–distortion interaction. The approach is verified for the NASA Stage 67 transonic fan. An example of the design process is also included; the model generated is shown to meet the desired fan stagnation pressure ratio and thrust to within 1%.

Highlights

In the design stage of an airframe, the external flow around all components must be considered.This is certainly important around engine nacelles, where the external flow will be affected by the operation of the fan
The results showed that the body force model with a compressibility correction was capable of matching the chordwise loading to within 7%, which was deemed as an acceptable level of accuracy for this design process
The thrust was lower than the thrust found by the 1D mass averaged take-off prediction code by 1.79%, which stemmed from the computational fluid dynamics (CFD) producing an fan stagnation pressure ratio (FPR) of 0.016 less than the 1D prediction

Summary

Introduction

In the design stage of an airframe, the external flow around all components must be considered. This is certainly important around engine nacelles, where the external flow will be affected by the operation of the fan. These simplified models use steady computational fluid dynamics (CFD) simulations for non-uniform inflow where normally unsteady simulations would be required. They reduce the number of grid cells needed by approximately two orders of magnitude within the turbomachinery blade rows [2]

Objectives

Results

Conclusion